It has been known for a long time that microbiologically loaded liquids such as waste water and drinking water may be treated by means of UV radiation. Here, even clarified waste water can be disinfected to such a degree that it may be introduced into rivers and bath waters. Drinking water can be disinfected by means of UV radiation, so that it is suitable for human consumption.
For disinfecting, low-pressure mercury radiators or medium-pressure mercury radiators are used, which are protected by cladding tubes and immersed into the water to be treated. The radiators and the cladding tubes are made from UV permeable material. In practice, quartz glass is used for this. The external surface of the cladding tubes is in direct contact with the surrounding liquid, and this is where any material depositing during operation over time separates from the surrounding liquid. This may be inorganic material such as, for example, lime. However, these may also be deposits of organic material.
As a result of the deposits on the external surfaces of the cladding tubes, the UV radiation emitted into the liquid will be reduced. In connection with the invention, reference will subsequently be made to an incrustation of the surface.
In order to remove such incrustations it was previously suggested to remove the radiators after an interruption of operation and then to clean the cladding tubes. It has also been suggested to clean radiators in closed channels in the case of an interruption of the liquid flow by flooding the channel with a liquid containing an acid. These solutions are not feasible for larger installations. Even an interruption of operation is disadvantageous.
Following that, various approaches for automatically cleaning the cladding tubes were developed. Each of these solutions is based on rings that are placed on top of the cylindrical cladding tubes and are then pushed along the cladding tubes by a drive. The mechanical contact between the ring and the cladding tube will then effect the cleaning. Depending on the application, various solutions have been proven to be feasible. In detail, the following solutions are known from the prior art:
U.S. Pat. No. 5,418,370 A, which is incorporated by reference, shows a cleaning device for a radiator cladding tube having a ring bearing against the cladding tube. The ring includes a chamber that is in communication with the cladding tube and into which a cleaning liquid is fed. Drive means are provided in order to move the ring along the cladding tube. In the course of this, the cleaning agent will gradually come into contact with the entire cladding tube surface and will effect there the removal of the incrustations. A similar solution is known from U.S. Pat. No. 6,013,917 A, which is incorporated by reference. Here, the cleaning ring includes two seals spaced from one another in the axial direction of the cladding tube, which seals seal the chamber against the surrounding liquid. Here it is suggested to feed the cleaning liquid into the chamber via a refill system, so that during a movement of the cleaning ring in the axial direction, the cleaning liquid will also come into contact with the surface over the entire length of the cladding tube and can separate the incrustations. What is problematic with this type of cleaning rings is the behaviour in the case of calcareous incrustations on the cladding tube surface. The chambers inside the rings are reliant on a seal against the surrounding liquid which is as good as possible. This seal gets damaged by calciferous incrustations, so that the cleaning liquid cannot be retained in the chamber and gets lost or an increased consumption occurs. In the case of drinking water applications it is also undesirable if substantial amounts of the cleaning liquid flow over into the drinking water.
DE 100 10 127 A1, which is incorporated by reference, suggests a cleaning ring, wherein the surface of the cladding tube is surrounded by an open-pored foam material. Cleaning liquid is fed into this foam material. Here, the elasticity of the foam material ensures that the cleaning ring will rest well against the surface of the cladding tube at all times. By virtue of the open pores, the cleaning liquid cannot escape into the surrounding water to an undesirable degree. This technical solution has proven to be useful for particularly calciferous water bodies. However, in continuous operation there is a risk that the cladding tubes will get scratched.
There are further cleaning rings that operate without the supply of cleaning liquid. These cleaning rings effect a purely mechanical cleaning of the cladding tube surface. Thus, a radiation system for the water of fish ponds is known from U.S. Pat. No. 5,942,109 A, which is incorporated by reference. What is suggested is a cleaning ring for a cladding tube of a UV radiator, which has brushes on the inside thereof. The brushes rest against the surface of the cladding tube and clean the cladding tube surface by means of an axial movement. For an application in the area of drinking water or waste water, such a solution has so far not been suggested. However, in continuous operation here, too, wear of the brushes and damage to the cladding tube surface have to be expected.
DE 600 19 306 T2, which is incorporated by reference, shows cleaning elements having elastomer rings and a chamber which is formed between two rings, respectively, into which rings a cleaning agent is to be fed.
DE 603 12 598 T2, which is incorporated by reference, shows a cleaning device comprising cleaning elements made from a wire material. The cleaning elements are elastically biased against the cladding tube surface and, during the cleaning operation, are driven in the axial direction of the cladding tube as well as additionally for rotation about the longitudinal axis.
Finally, DE 101 25 507 A1, which is incorporated by reference, shows a purely mechanically acting cleaning ring comprising a guide chamber and blades orientated vertically relative to the cladding tube surface in the guide chamber. The blades are configured as a helical ring which extends elastically around the cladding tube surface and, due to its elasticity, rests against the surface. This cleaning device adjusts itself to compensate for any wear. A high surface pressure of the cleaning ring against the cladding tube surface is achieved. However, in water bodies having a tendency to cause severe incrustations on the cladding tubes, the effect diminishes over time.
Therefore, no UV disinfection system is known from the prior art, wherein the cladding tube surface can be cleaned during running operation with a uniform effect even in the case of a high tendency to incrustations.